Dew forms when the temperature becomes equal to the dewpoint. This often happens first at ground level for two reasons. First, longwave emission causes the earth's surface to cool at night. Condensation requires the temperature to decrease to the dewpoint.

What time of day does dew fall?

Dew is most likely to form at night, as temperatures drop and objects cool. However, dew can form whenever a dew point is reached. Although warm, humid areas commonly experience heavy dew, dew does not form in amounts people could to collect as a water source.

What temperature does dew fall?

Most people are comfortable with a dew-point temperature of 60 degrees Fahrenheit (16 degrees Celsius) or lower. At a higher dew point of, for example, 70 F (21 C), most people feel hot or "sticky" because the amount of water vapor in the air slows the evaporation of perspiration and keeps the body from cooling.